Gas turbines are used in many areas to drive generators. Here, the energy content of a fuel is utilized to generate a rotary movement of a turbine shaft. For this purpose, the fuel is burnt in a number of burners, with compressed air being supplied by an air compressor. The combustion of the fuel generates a working medium that is at a high pressure and a high temperature. This working medium is passed into a turbine unit connected downstream of the burner, where it is expanded in a work-performing manner.
To transfer the momentum of the working medium to the turbine shaft, the turbine unit of a gas turbine has a number of rotatable rotor blades connected to the turbine shaft. For this purpose, the rotor blades are arranged in the form of a ring on the turbine shaft and therefore form a number of rotor blade rings or rotor blade rows. The turbine and the compressor are arranged on a common turbine shaft, also referred to as the turbine rotor, to which the generator is connected and which is mounted such that it can rotate about its center axis.
To route the flow of the working medium and to ensure the highest possible efficiency during the transfer of momentum to the rotor blades, the turbine unit usually also comprises a number of stationary guide vanes. These are attached to an inner housing or the stator of the turbine, likewise in the form of a ring, so as to form guide vane rings or guide vane rows. The rotor blades serve to drive the turbine shaft by transferring momentum from the working medium flowing through the turbine. By contrast, the guide vanes serve to route the flow of the working medium between in each case two rotor blade rows or rotor blade rings following one another as seen in the direction of flow of the working medium. A successive pair made of a ring of guide vanes or a guide vane row and a ring of rotor blades or a rotor blade row is also referred to in this context as a turbine stage.
A guide vane generally has a platform, also referred to as a vane root, which is arranged as a wall element for fixing the guide vane in question to the inner housing of the turbine and forms the outer boundary of a hot-gas duct for the working medium flowing through the turbine. For efficient routing of the flow of the working medium in the direction of a rotor blade row which follows a guide vane row, the guide vane usually also has a profiled vane blade formed integrally on the vane root. The vane blade extends between the vane root, on one side, and a cover plate formed integrally on the vane blade on the other side; this cover plate or shroud delimits the hot-gas duct for the working medium in the direction toward the turbine shaft in the region of the respective guide vane row. The vane blade and the vane root formed integrally thereon together with the cover plate likewise formed integrally thereon form a vane base body of the corresponding guide vane, which is usually of single-piece design. A vane base body of this type can be produced, for example, by casting, if appropriate also in single-crystal form.
In terms of specific design, i.e. in particular in terms of the selection of a suitable geometry, suitable dimensions and/or a suitable material, to ensure the highest possible efficiency of flow routing and transmission of momentum, it is desirable for guide vanes of this type to be specifically matched to the particular conditions and restricting factors at their location of use. Particularly in the case of gas turbines with combustion chamber systems that have a plurality of tubular combustion chambers arranged circumferentially distributed around the turbine shaft, this can lead to local fluctuations, differences and inhomogeneities in terms of the prevailing specific flow and temperature conditions in the circumferential direction around the turbine shaft. Therefore, in particular for the guide vanes belonging to what is described as the first guide vane row i.e. the guide vane row arranged between the combustion chamber and the first rotor blade row, as seen in the direction of flow of the hot gas, the incident flow onto and thermal stressing of the guide vane in question are relatively highly dependent on the precise installation position of the guide vane within the guide vane row.
To take account of these different conditions of use of the guide vane yet nevertheless to ensure a particularly high efficiency and high operational reliability for the gas turbine, it is customary, when designing the guide vanes, in particular with a view to a suitable selection of materials, to work on the basis of the most highly stressed guide vane in the particular guide vane row, so that the guide vanes which are exposed to less stress are usually designed with very high safety margins.
Alternatively, in gas turbines of this type, it is also possible to use systems in which individually adapted guide vanes are used in order to reduce the additional design and apparatus outlay associated with maintaining excessive safety margins. In systems of this type, guide vanes that are individually matched to the particular installation position are provided, but this requires increased numbers of spare parts to be kept in stock and, in particular for repair purposes, requires specific special manufacture of guide vanes that are matched to individual boundary conditions. Therefore, systems of this type can likewise only be achieved with high levels of technical and apparatus outlay.